*Editor's note: This idea is Brian's idea and based on conversations with him and Roger, but I just executed it.*

The length of academic courses has traditionally ranged between a few days for a short course to a few months for a semester-long course. Lectures are typically either 30 minutes or one hour. Term and lecture lengths have been dictated by tradition and the relative inconvenience of coordinating schedules of the instructors and students for shorter periods of time. As classes have moved online the barrier of inconvenience to varying the length of an academic course has been removed. Despite this flexibilty, most academic online courses adhere to the traditional semester-long format. For example, the first massive online open courses were simply semester-long courses directly recorded and offered online.

Data collected from massive online open courses suggest that shrinking both the length of recorded lectures and the length of courses leads to higher student retention. These results line up with data on other online activities such as Youtube video watching or form completion, which also show that shorter activities lead to higher completion rates.

We have some of the earliest and most highly subscribed massive online open courses through the Coursera platform: Data Analysis, Computing for Data Analysis, and Mathematical Biostatistics Bootcamp. Our original courses were translated from courses we offered locally and were therefore closer to semester long with longer lectures ranging from 15-30 minutes. Based on feedback from our students and the data we observed about completion rates, we made the decision to break our courses down into smaller, one-month courses with no more than two hours of lecture material per week. Since then, we have enrolled more than a million students in our MOOCs.

The data suggest that the shorter you can make an academic unit online, the higher the completion percentage. The question then becomes “How short can you make an online course?” To answer this question requires a definition of a course. For our purposes we will define a course as an educational unit consisting of the following three components:

** **

the distribution of educational material through lectures, audiovisual materials, and course notes**Knowledge delivery**-**.**

**Knowledge evaluation**- the evaluation of how much of the knowledge delivered to a student is retained.

**Knowledge certification**- an independent claim or representation that a student has learned some set of knowledge.

A typical university class delivers 36 hours = 12 weeks x 3 hours/week of content knowledge, evaluates that knowledge based on the order of 10 homework assignments and 2 tests, and results in a certification equivalent to 3 university credits.With this definition, what is the smallest possible unit that satisfies all three definitions of a course? We will call this smallest possible unit one knowledge unit. The smallest knowledge unit that satisfies all three definitions is a course that:

We will define a single unit of content as a text, image, or video describing a single concept.**Delivers a single unit of content**-

**Evaluates that single unit of content**- The smallest unit of evaluation possible is a single question to evaluate a student’s knowledge.

**Certifies knowlege**- Provides the student with a statement of successful evaluation of the knowledge in the knowledge unit.

An example of a knowledge unit appears here: https://jtleek.typeform.com/to/jMPZQe. The knowledge unit consists of a short (less than 2 minute) video and 3 quiz questions. When completed, the unit sends the completer an email verifying that the quiz has been completed. Just as an atom is the smallest unit of mass that defines a chemical element, the knowledge unit is the smallest unit of education that defines a course.

Shrinking the units down to this scale opens up some ideas about how you can connect them together into courses and credentials. I'll leave that for a future post.